Find the intervals on which ƒ(𝓍) = ∫ₓ¹ (t―3) (t―6)¹¹ dt is increasing and the intervals on which it is decreasing.
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- 0. Functions7h 52m
- Introduction to Functions16m
- Piecewise Functions10m
- Properties of Functions9m
- Common Functions1h 8m
- Transformations5m
- Combining Functions27m
- Exponent rules32m
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- Logarithmic Functions24m
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- Introduction to Trigonometric Functions38m
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- 1. Limits and Continuity2h 2m
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- 5. Graphical Applications of Derivatives6h 2m
- 6. Derivatives of Inverse, Exponential, & Logarithmic Functions2h 37m
- 7. Antiderivatives & Indefinite Integrals1h 26m
- 8. Definite Integrals4h 44m
- 9. Graphical Applications of Integrals2h 27m
- 10. Physics Applications of Integrals 3h 16m
- 11. Integrals of Inverse, Exponential, & Logarithmic Functions2h 34m
- 12. Techniques of Integration7h 39m
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- 16. Parametric Equations & Polar Coordinates7h 58m
8. Definite Integrals
Fundamental Theorem of Calculus
Problem 5.5.90
Textbook Question
Integrals with sin² 𝓍 and cos² 𝓍 Evaluate the following integrals.
∫₀^π/⁴ cos² 8θ dθ

1
Step 1: Recognize that the integral involves cos²(8θ). To simplify this, use the trigonometric identity cos²(x) = (1 + cos(2x)) / 2.
Step 2: Substitute the identity into the integral. The integral becomes ∫₀^(π/4) [(1 + cos(16θ)) / 2] dθ.
Step 3: Split the integral into two separate integrals: (1/2) ∫₀^(π/4) 1 dθ + (1/2) ∫₀^(π/4) cos(16θ) dθ.
Step 4: Evaluate the first integral, (1/2) ∫₀^(π/4) 1 dθ, which is straightforward as it represents the area under a constant function. For the second integral, (1/2) ∫₀^(π/4) cos(16θ) dθ, use the formula for the integral of cos(kx), which is (1/k) sin(kx).
Step 5: Apply the limits of integration (0 to π/4) to both parts of the integral. For the first part, calculate the result of (1/2) θ evaluated at the limits. For the second part, calculate (1/2) * (1/16) * sin(16θ) evaluated at the limits.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Trigonometric Identities
Trigonometric identities are equations involving trigonometric functions that are true for all values of the variables. Key identities include the Pythagorean identities, such as sin²(x) + cos²(x) = 1, and double angle formulas. These identities are essential for simplifying integrals involving sin²(x) and cos²(x), allowing for easier evaluation.
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Integration Techniques
Integration techniques are methods used to find the integral of a function. Common techniques include substitution, integration by parts, and using trigonometric identities to simplify the integrand. For integrals involving cos²(θ), applying the identity cos²(θ) = (1 + cos(2θ))/2 can transform the integral into a more manageable form.
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Definite Integrals
Definite integrals calculate the area under a curve between two specified limits. The notation ∫ₐᵇ f(x) dx represents the integral of f(x) from a to b. Evaluating definite integrals often involves finding the antiderivative of the function and applying the Fundamental Theorem of Calculus, which states that the definite integral can be computed by evaluating the antiderivative at the upper and lower limits.
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Definition of the Definite Integral
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